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07-23-2010, 09:55 AM   #61
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QuoteOriginally posted by falconeye Quote
We quote the first curtain stop event as one possible cause. Note however that you need an additional non-linear effect to cause a difference between a smooth and a hard stop. Both stops have the same "Kraftstoß" Ft (no direct English translation?).
I think that'd be "impulse", in the sense 4a here. Like "impulse drive" in Star Trek.

https://secure.wikimedia.org/wikipedia/en/wiki/Impulse_%28physics%29


Last edited by mattdm; 07-23-2010 at 11:18 AM. Reason: fix dictionary link
07-23-2010, 10:14 AM   #62
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QuoteOriginally posted by mattdm Quote
I think that'd be "impulse", in the sense 4a here. Like "impulse drive" in Star Trek.

https://secure.wikimedia.org/wikipedia/en/wiki/Impulse_%28physics%29
Thanks. "impulse" seems to be the only translation possible. The international sign "I" further emphasizes this.

My problem was that "impuls" in German means "momentum" in English and there is quite some confusion about the exact meaning of impulse. But "impulse as opposed to momentum" is the right translation. Thanks.
07-23-2010, 07:52 PM   #63
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QuoteOriginally posted by mattdm Quote
Like "impulse drive" in Star Trek.
Funny you bring up Star Trek as I'm thinking Falk could give Spock a run for his money.
07-25-2010, 02:44 AM   #64
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Has anyone ever thought of a shutter made of two spinning discs, each with a part cut out? The one disc would travel at a fast speed (according to the required shutter speed) whilst the one behind it spins at a slower speed. The exposure happens when the openings of the slower and the fast disc sync up over the sensor. That way you don't have to have abruptly stopping parts and therefore no shake, the discs can continue spinning or be braked gently magnetically.

It would require a bit more space though.

07-25-2010, 03:39 AM   #65
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QuoteOriginally posted by kari Quote
Has anyone ever thought of a shutter made of two spinning discs, each with a part cut out? The one disc would travel at a fast speed (according to the required shutter speed) whilst the one behind it spins at a slower speed. The exposure happens when the openings of the slower and the fast disc sync up over the sensor. That way you don't have to have abruptly stopping parts and therefore no shake, the discs can continue spinning or be braked gently magnetically.

It would require a bit more space though.
That's an interesting idea!

Everybody wanting to patent it: kari had it first!

If I understand correctly (you forgot to mention), the slower disc would have to have a larger opening (in proportion to ratio of speeds) and the faster disk's opening would have to be created by two disks of equal speed both with openings the size of the sensor or larger. Right? Otherwise, you would have no short exposure times. And of course, the opening would have to be much larger for long exposures. Ultimatily limited by the slower disks opening and ratio which means no long exposure times are possible. Except you stop disks in the middle of the exposure ... Or you make the disks spin at very different speeds for different shutter times.

So, a sweet patent probably hard to use
07-25-2010, 04:11 AM   #66
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another problem might be the actual size of such a system (a disc at least the diagonal of the frame in radius, if i understand this correctly, which is pretty big to fit into a dslr). interesting nonetheless (btw, a variation on this, if my memory doesn't fail me, had already been used long time ago, only it wasn't full rotation, and not a full disc. can't quite recall what it was called, i only have the image in my mind). perhaps one would rather go the whole mile at the end of the day, and use a central shutter instead .
07-25-2010, 04:15 AM   #67
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QuoteOriginally posted by falconeye Quote
That's an interesting idea!

Everybody wanting to patent it: kari had it first!

If I understand correctly (you forgot to mention), the slower disc would have to have a larger opening (in proportion to ratio of speeds) and the faster disk's opening would have to be created by two disks of equal speed both with openings the size of the sensor or larger. Right? Otherwise, you would have no short exposure times. And of course, the opening would have to be much larger for long exposures. Ultimatily limited by the slower disks opening and ratio which means no long exposure times are possible. Except you stop disks in the middle of the exposure ... Or you make the disks spin at very different speeds for different shutter times.

So, a sweet patent probably hard to use
Thanks! I did not really consider all the technicalities of different speeds yet, but I'm sure it can be possible, maybe if the discs spin in different directions you can get even faster shutter speeds. It would have to be stopped or slowed down for longer exposures, but if it's done with an electrical motor, it will not be a hard stop.

I just thought of it while I was in the shower now, us engineers have funny minds.
07-25-2010, 04:36 AM   #68
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i just tried to think of a way to make it smaller/more compact, and guess what: my brain came up with (a variation on) the classic cloth shutter (horizontal travel) design (like the leicas) ). just thought that was funny

07-25-2010, 08:40 AM   #69
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One remaining tidbit

In our study, we skipped a question which is now challenged by Oleg_V:

If the body shifts (and rotates around its center of gravity), then their are two possible causes of blur:

1. The body shifts but the sensor doesn't. This holds true because a pure shift doesn't cause blur at infinite distant subjects. So, if the sensor doesn't shift with the body, it causes blur.

2. The body+lens rotates. Here, if the sensor does shift with the body, it causes blur. And intuition would say that this is worse for longer focal lengths.

Both effects work in opposite directions. So, if a sensor moves slower than the body, then 1. comes into play but 2. is reduced.

So, the real question is about the magnitude of both effects. A question we have intentionally skipped in the study.


I now did a quick and dirty calculation (as posted at DPR), assuming a thin lens and idealising lens, body and shutter by a point masses each where the lens' center of gravity would be the thin lens' nodal points.

Warning: I may have made mistakes!!!

But this is the result I got:

1. Blur from body shift if sensor is NOT following ("s"):

s = m0/M y

where m0 is (effective) shutter mass, M total mass (shutter m0 + body m1 + lens m2). And y is the distance travelled by the shutter (~ the sensor height). That's the easy part. IF the sensor is following the body, body shift does NOT create blur for distant subjects.

2. Blur from body rotation if sensor IS following ("b"):

b = s (r0/r1) (1 + r0/r1 m2/m1) ~ m0/m1 y

where r0 and r1 are the distance of the shutter and the body to the overall center of gravity. If the shutter is located at the body's center of gravity, then r0/r1=1.

One can see (except if the shutter is in front of the body's center of gravity when looked at from the lens side):

b > s

So, the rotational blur should always dominate, whatever be the focal length. Therefore, a "soft" sensor coupling where the sensor crawls behind the body movement should reduce overall blur (as both sources counteract each other -- opposite signs). An active control would even have to move it in the opposite direction of the body movement (for large enough m2).

Of course, the entire calculation is more complex with true mass distributions (integrated inertial momenta) and compound lenses, especially those with a pupil magnification unequal 1!

Anybody able to confirm or carry further this calculation? In only used the preservation of rotational and linear momentum.

Some may wonder that the focal length cancels out and that a heavier lens doesn't help (m0/m1 does not contain the lens weight). So, my result may be of wider interest...


So far, I consider this a verification of some of the study's assumptions.


UPDATE:

I've run the calculation thru a math package, for easier verification and consultation by others:

-> http://www.falklumo.com/lumolabs/articles/k7shutter/CameraPitchTheory.pdf


Anybody wanting to model a compound lens?

Last edited by falconeye; 07-26-2010 at 04:40 AM.
07-26-2010, 04:23 PM   #70
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fighting lumo-blur, focus magic style ::

source files (.PEF)

1/60 = IMGP0889.PEF - File Shared from Box.net - Free Online File Storage

1/125 = IMGP0890.PEF - File Shared from Box.net - Free Online File Storage

1) out of ACR6.1, no sharpening (all sliders = 0)
2) motion blur horizontal 3px x 100%
3) motion blur vertical 1px x 100%
4) oof blur 1px x 50%

1/60 =




1/125 =


07-26-2010, 04:27 PM   #71
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and the lens was Sigma 24-135/2.8-4.5 (non EX series, 5x consumer grade zoom /means soft/, USD $100 cost, @ 135mm /means soft/, @ f5.6 /barely stopped down = means soft/)
07-27-2010, 12:27 AM   #72
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QuoteOriginally posted by kari Quote
Has anyone ever thought of a shutter made of two spinning discs, each with a part cut out? The one disc would travel at a fast speed (according to the required shutter speed) whilst the one behind it spins at a slower speed. The exposure happens when the openings of the slower and the fast disc sync up over the sensor. That way you don't have to have abruptly stopping parts and therefore no shake, the discs can continue spinning or be braked gently magnetically.

It would require a bit more space though.

Did you mean something like this: Rotary disc shutter - Wikipedia, the free encyclopedia ?
07-27-2010, 03:26 AM   #73
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Does distanse to the subject play a role?

I did some testing with my k7 and 35mm macro. I did see the blure issue in all my images exept in the macro photos.
07-27-2010, 03:51 AM   #74
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I wouldn't see why macro shots would do any better. I thought SR was less effective when dealing with macro distances.
07-27-2010, 05:24 AM   #75
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QuoteOriginally posted by gorankh Quote
Does distanse to the subject play a role?
I did some testing with my k7 and 35mm macro. I did see the blure issue in all my images exept in the macro photos.
In theory, yes. Classic shutter blur (where only the body moves) is caused by a combination of shift and rotation. The shift term-caused blur is dominant for high magnification macro (closer to 1:1) and the rotation term-caused blur is dominant for normal distances (small magnification << 1). Both terms, shift and rotation, normally are of similiar magnitude and therefore, classic shutter blur doesn't depend much on subject distance.

In the case of the K-7 where vibration seems to come into play additionally, it will be difficult to draw any conclusions without further tests. It would be further evidence that we don't see a case of pure classic shutter blur.

@Rondec: SR is not involved in all of this. Except maybe that the sensor is fixed by electromagnetic force rather than a screw. SR is less effective for macro (ineffective at 1:1) because it deals with the rotation term of human body shake only.

Last edited by falconeye; 07-27-2010 at 05:29 AM.
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